1. Field of the Invention
The present invention relates to an image sensing apparatus, control method thereof, and program.
2. Description of the Related Art
Conventional image sensing apparatuses such as a digital video camera include a display unit for displaying a sensed image, such as an electronic viewfinder (EVF) or liquid crystal display monitor. The user of the image sensing apparatus performs exposure control and focus adjustment while visually checking a sensed image on the display unit. However, most display units in image sensing apparatuses are small in size and are not suitable for strict exposure control and focus adjustment in terms of the display resolution.
From this, some image sensing apparatuses assist user operation by displaying an image for assisting exposure control or one for assisting focus adjustment, so as to be superimposed on a sensed image on the display unit. An example of the exposure control assist image is a pattern image (to be referred to as a “zebra pattern” hereinafter) of hatched lines, which is called a zebra pattern signal generated based on a preset luminance value and the luminance range of a sensed image. An example of the focus adjustment assist image is an edge image which is generated by extracting edge signals from a sensed image and is displayed to be superimposed on a sensed image. The edge image is obtained by edge correction, peaking, or enhancer (to be referred to as “peaking” hereinafter).
For example, the luminance range for displaying a zebra pattern is set to a predetermined level convenient for stop adjustment. In general, the threshold of the luminance level or a predetermined luminance level range is set according to IRE (Institute of Radio Engineers) used as a unit representing the amplitude of a video signal. The IRE has originally meant a standard defined by the Institute of Radio Engineers (IEEE now), and is generally used as a unit. The IRE defines pedestal level (black)=0 IRE (in some cases, black=7.5 IRE), and white=100 IRE. When manually controlling the exposure, the luminance level range is set to about 70 IRE to 100 IRE. A zebra pattern is displayed to be superimposed in the image area of a sensed image that corresponds to this range.
Japanese Patent Laid-Open No. 4-328964 is known as a technique of displaying an assist image to be superimposed on a sensed image. Japanese Patent Laid-Open No. 4-328964 discloses a technique of displaying zebra patterns in the image area of a signal strength equal to or higher than an arbitrary luminance level and that of a signal strength equal to or lower than the luminance level.
The conventional technique simply displays an assist image to be superimposed in an image area or in-focus area which satisfies a predetermined luminance condition. This technique displays an assist image even in an image area overlapping an object area having a predetermined feature, like a face area containing a person's face.